Method of depositing material

ABSTRACT

Material is deposited in a desired pattern by spontaneous deposition of precursor gas at regions of a surface that are prepared using a beam to provide conditions to support the initiation of the spontaneous reaction. Once the reaction is initiated, it continues in the absence of the beam at the regions of the surface at which the reaction was initiated.

This application is a continuation of U.S. patent application Ser. No.13/017,015, filed Jan. 30, 2011, which is incorporated by referenceherein.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method and apparatus for depositingmaterial in a pattern that includes features on a microscopic ornanoscopic scale.

BACKGROUND OF THE INVENTION

Beam systems, such as electron beam systems, ion beam systems, laserbeam systems, cluster beam systems, and neutral particle beam systems,are used to create features on a surface by etching or depositingmaterial. Beam-induced deposition processes typically use a precursorgas that reacts in the presence of the beam to deposit material on thesurface in areas where the beam impacts. For example, a gaseousorganometallic compound, such as tungsten hexcarbonyl, is provided nearthe sample and is adsorbed onto the surface. The organometallic compounddecomposes in the presence of a beam, such as an ion beam or an electronbeam, to form a metal that remains on the surface and a volatile organiccompound that is removed by a vacuum pump. Because the precursor isstable, that is, it does not spontaneously decompose on the surface inthe absence of the beam, a fine structure can be deposited, with thefeature size of the structure determined by the beam size and thebeam-sample interaction volume.

Two disadvantages of charged particle beam-induced deposition are lowdeposition rates and carbon contamination of the deposit. While chargedparticle beams can typically be made much smaller than a laser beam, thesize of the beam spot on the work piece, is typically inverselyproportional to the current in the beam. A small, high resolution beam,therefore, has a low current, which produces a low deposition rate. Therate of electron beam-induced deposition is typically between about5×10⁻⁴ um³·nC⁻¹ to about 5×10⁻³ um³·nC⁻¹.

Precursor gases for charged particle beam deposition are typicallycarbon containing metallo-organic compounds. Carbon from the precursors,or from other sources such as lubricants in the vacuum chamber,typically contaminates the deposited metallic material, greatlyincreasing the resistivity of the deposit. The slow deposition rate andthe high resistivity are undesirable for nanoprototyping andnanoresearch applications.

Various techniques have been tried to improve the purity of beam-induceddeposits, but have met with limited success. Such techniques includeheating the work piece during deposition, annealing the deposit afterdeposition, mixing the precursor gas with reactive gases during or afterdeposition, and using carbon-free precursors. An over view of techniquesused to deposit a pure material is provided in A. Botman, et al.,“Creating pure nanostructures from electron-beam-induced depositionusing purification techniques: a technology perspective,” Nanotechnology20 372001 (2009).

Pure deposits have been achieved in electron beam-induced deposition inultra high vacuum systems, but such systems significantly increase costand the deposit rate is still low. Contamination reduction has also beenachieved in electron or ion beam-induced deposition by mixing adeposition precursor with an oxidizer such as O₂ or H₂O, as described,for example, in Folch et al, Appl Phys. Lett. 66, 2080-2082 (1995) andMolhave et al, Nano Lett. 3, 1499-1503 (2003)). Use of an oxidizer isoften undesirable because it results in oxide formation or incompletereduction of the precursor gas.

Attempts to use hydrogen gas to improve the purity and deposition rateof iron deposited from Fe(CO)₅ have been unsuccessful, perhaps becauseof the low sticking coefficient and/or short residence times on commonsurfaces; H. Wanzenboeck et al, presented at International Conference onElectron, Ion, and Photon Beam Technology and Nanofabrication (EIPBN)2008. The current state of the art of electron beam-induced depositionis described, for example, in Randolph et al, “Focused NanoscaleElectron-Beam-Induced Deposition and Etching,” Critical Reviews in SolidState and Materials Sciences, 31:55-89 (2006).

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved deposition process.

Deposition of a localized pattern is achieved, for example, by producinglocal conditions conducive to a spontaneous deposition reaction in thedesired pattern, while global conditions on the work piece are notconducive to the spontaneous reaction. In accordance with some preferredembodiments, the spontaneous decomposition reaction can deposit arelatively pure material in a microscopic or nanoscopic scale pattern.Unlike prior art beam deposition processes in which the beam is requiredto sustain the reaction, in embodiments of the present invention, thebeam produces local conditions that are conducive to the initiation of aspontaneous reaction that continues after the beam ceases.

In some embodiments, a beam is directed toward a work piece to prepare awork piece surface so that the work piece includes portions that supportthe initiation of a spontaneous deposition reaction and portions that donot support the initiation of the spontaneous deposition reaction.Multiple gases, typically including a precursor gas and an activatorgas, are provided at the work piece surface, the gases spontaneouslyreacting with each other to deposit a material at the regions at thesurface that support the initiation of the spontaneous depositionreaction without depositing material at the portions of the work piecethat do not support the initiation of the spontaneous depositionreaction, to selectively deposit material in a pattern onto the workpiece surface.

In some embodiments, the products of the spontaneous reaction betweenthe precursor gas and activator gas can include a compound which uponinteraction with the substrate or work piece material causes an etchingreaction instead of a deposition. As a result, some amount of thesubstrate, sample or work piece is chemically removed.

In some embodiments, the global reaction is suppressed by elevating thework piece temperature globally, which reduces the adsorption of thereactants across the work piece. A local reaction induced by an electronbeam provides a nucleation site that locally lowers the reaction barrierand the initial deposit then acts like a catalyst for the subsequentreaction. In another embodiment, the surface is locally modified, forexample, by impact of an ion beam, and the reaction is initiated only onthe modified surface.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter. It should be appreciated by those skilled in the art thatthe conception and specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the present invention. It should alsobe realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more thorough understanding of the present invention, andadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a charged particle beam system that can be used toimplement the present invention.

FIG. 2 is a flow chart showing the steps of an embodiment of theinvention.

FIG. 3A is a photomicrograph of a pattern shortly after the depositionwas initiated by an electron beam. FIG. 3B is a photomicrograph of thedeposit of FIG. 3A taken about one minute after the photomicrograph ofFIG. 3A.

FIG. 4 is a flow chart showing a method of filling a via.

FIG. 5 show a cross section of a via produced by the method of FIG. 4.

FIG. 6 is a flow chart showing a method of producing a protective layer.

FIG. 7A is a photomicrograph of a protective layer deposited accordingto the method of FIG. 6. FIG. 7B is a photomicrograph showing a crosssection of the protective layer of FIG. 7A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with a preferred embodiment of the present invention, aspontaneous decomposition reaction involving two or more species resultsin rapid deposition of a high purity material. Some embodiments mix twochemicals, a precursor and an activator, that react spontaneously andwould therefore have been considered incompatible in the prior art. Insome embodiments, the reactants react spontaneously to fully decompose ametal-containing reactant to deposit an essentially pure metal onto thesubstrate, sample or work piece. In other embodiments, the reactioncauses etching of the substrate, sample or work piece.

Embodiments of the invention deposit material in a pattern by providinglocal conditions in the desired pattern to enable the spontaneousdecomposition reaction, while maintaining conditions that inhibit thereaction on the rest of the work piece surface. The reaction may beinhibited globally, for example, by decreasing the surface residencetime of the species, which can be achieved by increasing the work piecetemperature, or by providing a material on the surface that inhibits thereaction. A deposition pattern may be defined locally, for example, bycreating initial seeds or nucleation sites in the desired pattern on thework piece, for example, by a beam, such as a photon beam (e.g., a laserbeam) or a charged particle beam to impinge on the surface in thedesired pattern. The beam is thought to enable the local deposition byaltering the surface, such as by removing contamination, removing anative oxide layer, creating surface features that act as nucleationsites or providing additional energy.

The global conditions at the work piece surface are sufficiently closeto the conditions required to support the reaction so that once thereaction has been initiated, the reaction can continue in the absence ofthe beam until at least one of the reactants is no longer available insufficient quantity to sustain the reaction. The initial deposit acts asa catalyst for subsequent reactions to continue the deposition. In manyembodiments, the beam does not include material that is deposited ontothe surface to catalyze the reaction; instead the beam itself acts asthe catalyst, alters the surface or provides energy to initiate thereaction.

Some embodiments of the invention are essentially a form of lowtemperature chemical vapor deposition (CVD) in which a precursoradsorbate is decomposed by an activator chemical leading to rapid growthof a pure material. Some embodiments work well with the reaction beinginitiated at room temperature; some embodiments were tested and workedat temperatures elevated by several tens of degrees. For example, insome embodiments the deposition is initiated while the work piecesurface is maintained at a temperature of less than or about 200° C.,less than or about 100° C., or less than or about 60°. In preferredembodiments of the invention, applicants believe that the depositionreaction takes place only at the sample surface, not in the gas, andtakes place only when the concentrations of both precursor species arewithin a “growth window.” To localize the deposition process the growthwindow can be broadened locally, such as by electron, ion, or laserirradiation, so that the local conditions at the sample are within thebroadened growth window. The growth window is dependent on conditions atthe sample surface, such as surface composition and morphology, that is,shape, structure, and texture.

The deposition rate varies with the embodiment and can vary, forexample, depending on the relative and absolute abundance of theprecursor and activation chemicals, the work piece temperature, themethod of nucleation, and other factors. The deposition rate istypically independent of the charged particle beam current or laser beamfluence used to initiate the reaction.

FIG. 1 depicts an exemplary dual beam system 102 that can be used tocarry out embodiments of the invention. Suitable dual beam systems arecommercially available, for example, from FEI Company, Hillsboro, Oreg.,the assignee of the present invention. While an example of suitablehardware is provided below, the invention is not limited to beingimplemented in any particular type of hardware.

Dual beam system 102 has a vertically mounted electron beam column 104and a focused ion beam (FIB) column 106 mounted at an angle ofapproximately 52 degrees from the vertical on an evacuable specimenchamber 108. The specimen chamber may be evacuated by pump system 109,which typically includes one or more, or a combination of, aturbo-molecular pump, oil diffusion pumps, ion getter pumps, scrollpumps, or other known pumping means.

The electron beam column 104 includes an electron source 110, such as aSchottky emitter or a cold field emitter, for producing electrons, andelectron-optical lenses 112 and 114 forming a finely focused beam ofelectrons 116. Electron source 110 is typically maintained at anelectrical potential of between 500 V and 30 kV above the electricalpotential of a work piece 118, which is typically maintained at groundpotential.

Thus, electrons impact the work piece 118 at landing energies ofapproximately 500 eV to 30 keV. A negative electrical potential can beapplied to the work piece to reduce the landing energy of the electrons,which reduces the interaction volume of the electrons with the workpiece surface, thereby reducing the size of the nucleation site. Workpiece 118 may comprise, for example, a semiconductor device,microelectromechanical system (MEMS), or a lithography mask. The impactpoint of the beam of electrons 116 can be positioned on and scanned overthe surface of a work piece 118 by means of deflection coils 120.Operation of lenses 112 and 114 and deflection coils 120 is controlledby scanning electron microscope power supply and control unit 122.Lenses and deflection unit may use electric fields, magnetic fields, ora combination thereof.

Work piece 118 is on movable stage 124 within specimen chamber 108.Stage 124 can preferably move in a horizontal plane (X and Y axes) andvertically (Z axis) and can tilt approximately sixty (60) degrees androtate about the Z axis. A door 127 can be opened for inserting workpiece 118 onto X-Y-Z stage 124 and also for servicing an internal gassupply reservoir (not shown), if one is used. The door is interlocked sothat it cannot be opened if specimen chamber 108 is evacuated. Stage 124may be cooled, for example, by a Peltier cooler (not shown) or heatedby, for example, a resistive heater 126.

Mounted on the vacuum chamber are multiple gas injection systems (GIS)130 (two shown). Each GIS comprises a reservoir (not shown) for holdingthe precursor or activation materials and a needle 132 for directing thegas to the surface of the work piece. Each GIS further comprises means134 for regulating the supply of precursor material to the work piece.In this example the regulating means are depicted as an adjustablevalve, but the regulating means could also comprise, for example, aregulated heater for heating the precursor material to control its vaporpressure.

When the electrons in the electron beam 116 strike work piece 118,secondary electrons, backscattered electrons, and Auger electrons areemitted and can be detected to form an image or to determine informationabout the work piece. Secondary electrons, for example, are detected bysecondary electron detector 136, such as an Everhard-Thornley detector,or a semiconductor detector device capable of detecting low energyelectrons. Signals from the detector 136 are provided to a systemcontroller 138 that controls a monitor 140, which is used to displayuser controls and an image of the work piece using the signal fromdetector 136.

The chamber 108 is evacuated by pump system 109 under the control ofvacuum controller 141. The vacuum system provides within chamber 108 avacuum of approximately 3×10⁻⁶ mbar. When a suitable precursor oractivator gas is introduced onto the sample surface, the chamberbackground pressure may rise, typically to about 5×10⁻⁵ mbar. The localpressure and gas concentration at the work piece surface aresignificantly greater than the background pressure and concentration.See, for example, Randolph et al. above, which determines the localpressure at a work piece surface.

Focused ion beam column 106 comprises an upper neck portion 144 withinwhich are located an ion source 146 and a focusing column 148 includingextractor electrode 150 and an electrostatic optical system including anobjective lens 151. Ion source 146 may comprise a liquid metal galliumion source, a plasma ion source, a liquid metal alloy source, or anyother type of ion source. The axis of focusing column 148 is tilted 52degrees from the axis of the electron column. An ion beam 152 passesfrom ion source 146 through focusing column 148 and betweenelectrostatic deflectors 154 toward work piece 118.

FIB power supply and control unit 156 provides an electrical potentialat ion source 146. Ion source 146 is typically maintained at anelectrical potential of between 1 kV and 60 kV above the electricalpotential of the work piece, which is typically maintained at groundpotential. Thus, ions impact the work piece at landing energies ofapproximately 1 keV to 60 keV. FIB power supply and control unit 156 iscoupled to deflection plates 154 which can cause the ion beam to traceout a corresponding pattern on the upper surface of work piece 118. Insome systems, the deflection plates are placed before the final lens, asis well known in the art. Beam blanking electrodes (not shown) withinion beam focusing column 148 cause ion beam 152 to impact onto blankingaperture (not shown) instead of work piece 118 when a FIB power supplyand control unit 156 applies a blanking voltage to the blankingelectrode.

The ion source 146 typically provides a beam of singly charged positivegallium ions that can be focused into a sub one-tenth micrometer widebeam at work piece 118 for modifying the work piece 118 by ion milling,enhanced etch, material deposition, or for imaging the work piece 118.

System controller 138 controls the operations of the various parts ofdual beam system 102. Through system controller 138, a user can causeion beam 152 or electron beam 116 to be scanned in a desired mannerthrough commands entered into a conventional user interface (not shown).Alternatively, system controller 138 may control dual beam system 102 inaccordance with programmed instructions. FIG. 1 is a schematicrepresentation, which does not include all the elements of a typicaldual beam system and which does not reflect the actual appearance andsize of, or the relationship between, all the elements.

FIG. 2 shows a flowchart 200 describing the steps of one embodiment ofthe invention. Surface conditions favorable to the initiation of adeposition reaction are created in a desired pattern. In someembodiments, as shown in the right branch of the flow chart in FIG. 2,the pattern is created and then the reactants are introduced. In otherembodiments, such as the one shown in the left branch, the pattern iscreated while the reactants are present at the surface.

In step 202, a work piece is positioned in a sample vacuum chamber. Instep 204, the chamber is evacuated. In step 206, on the left branch, thework piece is optionally heated slightly above room temperature, forexample, to about 60° C. The work piece preferably remains at a fixedtemperature for the entire time that the reactants are in the chamber.Applicants believe that the reaction requires a sufficient quantity ofeach of the reactants, within a specified ratio range, adsorbed onto thesurface for the reaction to initiate. Heating is thought to reduce thelikelihood of a spontaneous reaction of the reactants by reducing thesticking coefficient of the reactants so that there is insufficientreactant on the surface to initiate the reaction without a beam-inducedalteration of local conditions.

In step 210, the reactants are introduced into the sample vacuumchamber, for example, through separate gas injection system (GIS)needles. For deposition to occur, both gases should be presentsimultaneously at the sample, and the ratio of the gases should becontrolled within a range. In one embodiment, Pt(PF₃)₄ gas is injectedinto the chamber through one GIS needle and XeF₂ is injected into thechamber through a second GIS needle. The partial pressures of Pt(PF₃)₄and XeF₂ are between 1×10⁻⁷ mbar and 1×10⁻² mbar. The ratio of Pt(PF₃)₄pressure to XeF₂ pressure is preferably between 1:1000 and 1000:1.

Other gases that may be used as precursor gases include, for example,Ni(PF₃)₄, Cr(PF₃)₆, Fe(PF₃)₅. Other gases that may be used as theactivator gas include Cl₂ and F₂. Preferred precursor gases such asmetal-organic compounds, metal-organic compounds with carbonyl groups,inorganic compounds with metal ligands, or metal compounds withfluorophosphine groups preferably decompose completely to produce anessentially pure deposit and one or more volatile compounds. Otherdesirable properties of a precursor gas include a vapor pressure greaterthan the base pressure of the vacuum system, and a high degree ofchemical stability in the absence of an activator gas.

Preferred activator gases such as halogen-containing compounds, orhighly oxidizing or reducing agents preferably react with the precursorgas to decompose completely to produce a pure deposit and one or morevolatile compounds. Other desirable properties of an activator gasinclude a vapor pressure greater than the base pressure of the vacuumsystem, and a high degree of chemical stability in the absence of aprecursor gas. Such gases include XeF₂, Cl₂ or F₂.

In step 212, nucleation sites are produced that will induce the gases toreact spontaneously at the sites. In one embodiment, an electron beam isdirected toward the work piece while the reactant gases are present, theelectron beam being directed in a pattern that corresponds to thedesired deposition pattern. The electron beam is preferably used in spotmode with a long, single-pass dwell time on the order of milliseconds orseconds at each dwell point, to create a spot mode deposit. The gasesbegin to react spontaneously at the spot where the electron beam hitsthe work piece surface, creating a nucleation site. An ion beam, laserbeam, or other type of beam could also be used in step 212. In step 214,the beam is discontinued after creation of the pattern of nucleationsites. The reaction will continue in the absence of the beam at thesites where nucleation occurred as long as reactants are present inadequate quantities, that is, at adequate concentrations or partialpressures to sustain the reaction, the reaction subsequently beingcatalyzed by previously deposited material.

In another embodiment, as shown in the right branch of the flow chartshown in FIG. 2, the nucleation sites are produced before the reactantsare introduced. In step 220, nucleation sites are produced for example,by directing a beam of ions, such as gallium ions from a liquid metalion source, in a pattern onto the surface of the work piece or bydirecting a beam of photons toward the work piece before providingmultiple gases at the work piece surface. The ion beam is thought toaffect the surface morphology by increasing the surface roughness, tocreate the nucleation sites. In step 222, the beam is discontinued andin step 224 the work piece is optionally heated. Alternately, the workpiece may be heated while the nucleation sites are created. In step 226,the reactants are introduced into the vacuum chamber near the samplesurface.

At this point in both branches, nucleation sites have been created andreactants are present at the surface. Applicants have found that thewhen the reactants are introduced into the vacuum chamber, they willinitially spontaneously decompose at the nucleation sites. After theinitial growth at the nucleation site, further spontaneous decompositiontakes place on freshly-decomposed material, thereby causing overallgrowth to proceed radially outwards from each nucleation site.

In some experiments, applicants have found that the resistivity of thedeposited platinum film was around 1000 μΩ-cm. This resistivity isconsiderably higher than the bulk resistivity of pure platinum, which isabout 10 μΩ-cm. Applicants believe that the higher measured resistivityoccurs because the deposited films included voids, that is, they werenot fully dense. FIB cross sections made of some films support thishypothesis by showing voids in the deposited material. Applicants foundthat the resistivity of the deposited film can be significantly loweredby applying a focused ion beam to the film as it is being deposited tocompress or “densify” the deposited material and reduce or eliminatevoids.

In optional step 228, an ion beam, such as a beam of gallium ions from aliquid metal ion source or argon ions from a plasma ion source, isdirected toward the work piece where the deposition is occurring toincrease the density of the deposited material. The ion beam preferablyirradiates the deposit in “flood mode,” that is, with low magnificationand the highest available current. Applicants have found that highergallium ion current leads to better conductivity. Applicants interpretthis result as showing that the impact of the gallium ions densifies theplatinum film. Applicants have produced platinum films that haveresistivities of about 60 μΩ-cm using a 4.3 nA gallium ion beam current.Lower resistivities may potentially be attainable using higher beamcurrents. Using a noble gas to densify the deposit eliminates theimplantation of gallium atoms, which may be desirable in someapplications.

In decision block 230, it is determined whether sufficient material hasbeen deposited. The amount of material deposited can be calculated byknowing the deposition rate and measuring the time that sufficientconcentrations of reactants have been in the chamber, or by measuring aproperty of the coating, such as resistivity, that correlates tothickness. Another method of determining film thickness is described inU.S. Pat. No. 6,399,944 to Vasilyev, et al. for “Measurement of filmthickness by inelastic electron scattering,” which is assigned to theassignee of the present invention.

If sufficient material has not been deposited, then reactants arecontinued to be introduced to the work piece surface in step 232. Ifsufficient material has been deposited, the flow of reactants is stoppedin step 234. For example, the delivery of XeF₂ can be rapidly stoppedonce the deposit has grown sufficiently. It will be understood that theability to stop the reaction depends on the rate at which the gas isexhausted from the chamber by the chamber vacuum pump and the pressureof the reactant during processing.

FIGS. 3A and 3B are photomicrographs of platinum deposits made inaccordance with an embodiment of the present invention. FIG. 3A shows animage of a platinum pattern 302 taken shortly after the electron-beaminduced seeding in accordance with the process in the left column ofFIG. 2 using Pt(PF₃)₄ and XeF₂. FIG. 3B shows the same pattern 302 afterletting the deposit grow spontaneously for about a minute in the absenceof an electron beam. FIGS. 3A and 3B demonstrate how the final patternis a direct result of the seeding performed by the electron beam. Randomdeposition at points such as point 304 is thought to be caused bypreexisting surface defects that act as nucleation sites.

Unlike prior art electron beam-induced deposition, ion beam-induceddeposition, and laser-induced deposition, in which the deposition occursonly in the presence of the beam, deposition in the present inventioncontinues at each point that was “seeded” by the beam after the beam isdiscontinued. Thus deposition can be much faster, because material isbeing deposited simultaneously at every nucleation site, even after thebeam has moved to the next site in the scan pattern. Thus, while asingle beam can only impact a single dwell point at a time, depositionin the present invention can occur simultaneously and continuously atmany points across the work piece surface.

The spontaneous reaction is thought to occur on the surface of the workpiece after the gases are adsorbed, and not in the gas phase. Thereaction rate is dependent on the work piece surface temperature and therelative and absolute abundance of both gases. In an embodiment usingPt(PF₃)₄ as the precursor gas and XeF₂ as the activator gas to depositplatinum, the deposition rate has been measured at fifty cubic micronsper second and the material deposited has an energy dispersive x-rayanalysis spectrum which is indistinguishable from that of pure platinum.

Applicants have found that some deposited films tend to delaminate andthicker films tend to crack. This may be further evidence of thedeposited material's high purity. It is thought that the amount ofdelamination is also dependent on the adhesion of the film to the workpiece. For example, adhesion of the metallic films to silicon appears tobe substantially better than the adhesion of films to silicon dioxide.Growing the films more slowly is desirable to create high-density filmsand avoid cracking, although applicants have found that there appears tobe a minimum growth rate for any particular set of conditions. Filmsgrown at room temperature show a higher propensity to delamination thanthose grown at work piece temperatures of, for instance, 60° C., thoughcracking was observed for the latter also.

Embodiments of the present invention can be used in a wide variety ofapplications in which a material is deposited onto a target surface of awork piece. One application is in “circuit edit,” a process by whichintegrated circuits are modified to test wiring changes before creatingnew photolithography masks to mass produce the circuit. It is known touse an ion beam to sever electrical connections by cutting conductorsand to use ion beam-assisted deposition to create new connections.Electrical connections are made between conductors in differentconductive layers separated by insulating layers by milling a hole,referred to as a “via,” between the conductive layers using the ion beamand filling the hole with a conductive material. The hole may be filled,for example, by ion beam-assisted deposition or electrochemicaldeposition as described in U.S. Pat. Pub. No. 20050227484 to Gu et al.for a “System for Modifying Small Structures,” which is assigned to theassignee of the present invention.

FIG. 4 shows a flow chart 400 a method of filling a via with aconductive material. In step 402, a semiconductor circuit to be modifiedis placed in a vacuum chamber of a focused ion beam system, preferably adual beam system having both an ion column and an electron column foruse in scanning electron microscopy. In step 404, the sample chamber isevacuated. In step 406, the location at which the via is to be createdis identified. The location can be determined, for example, by usingsurface features visible in an SEM image or focused ion beam image, andcomparing the observable features with computer aided design data.

In step 408, the via is milled using the focused ion beam. It ispreferable to mill using an etch-enhancing gas, such as XeF₂ or iodine,to reduce redeposition of the milled material onto the sidewalls of thehole being milled. In step 410, two reactants, a precursor gas and anactivator gas, are introduced into the vacuum chamber. As describedabove with respect to the right hand column of FIG. 2, the reactantswill tend to spontaneously react and deposit a material on regions thatwere impacted by the ion beam. Because the via was milled using the ionbeam, the gases tend to react in the via and deposit material. Anadvantage of this method is that the film grown by the spontaneousreaction will preferentially nucleate inside the via, filling it beforesubstantial growth begins on the top surface of the work piece. It ispreferred to perform steps 408 and 410 in the same vacuum chamber, i.e.that the work piece not be exposed to air between these two steps ofmilling and reactant introduction; this precaution maximizes thepreferential nucleation in the just-made via with respect to the rest ofthe work piece. An additional precaution would be to perform step 410within a reasonably short amount of time of step 408, for instance notto exceed a few hours or preferably 30 minutes, for the same reason. Instep 412, it is determined whether or not the via has been filled, forexample, by observing the via using a scanning electron microscope(“SEM”). If the via is not yet filled, reactants are continued to beintroduced into the vacuum chamber. When the via had been filled, theintroduction of reactants is stopped in step 414. The concentration ofreactants will decrease as gases are exhausted by the vacuum pump, andthe reaction will stop when the concentration or partial pressure of oneof the reactants is insufficient to sustain the reaction.

FIG. 5 is a photomicrograph of a cross section of a via filled inaccordance with the method of FIG. 4 using Pt(PF₃)₄ as the precursor gasand XeF₂ as the activator gas. Filling a via having a 5:1 aspect ratiois readily achieved using the present invention. Skilled persons will beable to fill holes having aspect ratios of 10:1 or greater using anoptimized process. The resistance through these vias has been measuredto be in the range 10 to 70 Ohm depending on via size. Resistivity isdifficult to reliably measure in this geometry.

Applicants have found that in some embodiments, the resistance of thefilled via is greater than the resistance expected of a solid plug ofpure platinum, probably because (a) there may be voids in the via as canbe seen from the cross-section images; (b) the deposition material islikely in non-dense form and thus has a higher resistivity, and it isdifficult to densify the material in the via using the ion beam; (c) thecontact resistance at the interface with the existing conductors may begreater than the contact resistance of a conductor deposited by to FIBdeposition or FIB sputter deposition, perhaps because there is little orno mixing of materials at the interface.

Another application of the present invention is the deposition of aprotective layer to protect a sample during further processing. Forexample, to prevent changes to a structure while preparing it forobservation, it is common to apply a protective layer to the surface ofa semiconductor before cutting a cross section for SEM viewing or beforecutting out a lamella for viewing on a transmission electron microscope.The protective layer is typically applied by a combination of electronbeam-induced deposition and ion beam-induced deposition. Ionbeam-induced deposition has a higher deposition rate than electron-beaminduced deposition, but the gallium ions implant into the work piece anddamage the work piece surface. A two-step process is sometimes used toreduce damage and improve processing speed: a protective layer, such asa platinum layer, is deposited using electron beam-induced deposition,followed by the deposition of a thicker layer using ion beam-induceddeposition. The layer deposited by the electron beam serves to protectthe area from gallium implantation and damage during the subsequent stepof depositing a protective layer with the gallium beam. The lowdeposition rate of the electron beam-induced deposition and therequirement to use both an ion beam and an electron beam is a drawbackto this process.

The spontaneous reaction of the present invention allows the rapiddeposition of a protective layer over an area of interest without ionbeam damage. FIG. 6 shows a flowchart 600 showing the steps of a methodof applying a protective layer. In step 602, the work piece is placed ina vacuum chamber of a dual beam system having both an ion column and anelectron column. In step 604, the sample chamber is evacuated. In step606, region of interest is located on the work piece. For example, itmay be desirable to observe a vertical cross section at a specifiedlocation, and the position of the cross section can be determined usingsurface features visible in an SEM image or focused ion beam image, andcomparing the observable features with computer aided design data.

In step 608, the sample is optionally heated to, for example, 60 degreesto prevent or reduce unwanted deposition by reducing the residence timeof gas molecules on the work piece surface. In step 610 reactants areintroduced, usually by separate gas injection pathways, into the vacuumchamber near the surface of the work piece. In step 616, an electronbeam is optionally scanned over the area identified in step 606. Forexample, the electron beam may be scanned in such a manner as to observethe reaction proceed. If the electron beam is used for observation thenthe growth will initiate from a random nucleation point and proceed togrow to a large size. The electron beam may alternatively be used toinitiate a spontaneous reaction of the reactants in the scan area. Instep 618, if the electron beam was used for nucleation of the growth ina pattern form, it is discontinued, while the reaction continues,catalyzed by the initial deposit; otherwise it may be left on to observethe growth proceed to desired completion. When the protective layer issufficiently thick, as determined in decision block 620, introduction ofthe reactants is discontinued in step 622, and the reaction will ceaseas the concentration of one of the reactants falls below a minimumlevel. In step 624, an ion beam is directed towards the work piece toprepare a portion of the region of interest for analysis. For example,the ion beam can free a microsample from the work piece, attach themicrosample to a TEM sample holder, and thin the sample in preparationfor viewing on a transmission electron microscope (“TEM”).Alternatively, the ion beam can mill a groove to expose a cross sectionfor viewing by an SEM.

FIG. 7A shows a top view of a film that was deposited using the methodof FIG. 6 using Pt(PF₃)₄ as the precursor gas and XeF₂ as the activatorgas. The layer shown in FIG. 7 was deposited in approximately 90seconds, has a diameter of hundreds of microns diameter and a thicknessof about 200 nm.

In another embodiment, surface conditions are altered by providing aninitial patterned film on the surface to initiate or inhibit thespontaneous reaction of the reactants, to deposit a film defined by theinitial pattern. For example, the initial film can be produced bybeam-induced deposition or by etching a pattern in a masking material bya beam. For example, carbon requires a different ratio of activator toprecursor gas in order to nucleate the growth of metal from someprecursor-activator combinations, such as Pt(PF₃)₄ and XeF₂. A patterncan be deposited by providing an initial pattern of carbon on thesurface, with the subsequent deposition occurring in regions in whichcarbon is not present. The carbon mask can later be removed. Carbon canbe deposited, for example, by direct writing using an ion or electronbeam-induced deposition, for example, using a styrene precursor. Carboncan be deposited by direct writing of carbon using a beam of fullerenes,as described, for example, in U.S. Pat. Publication No. 2008/0142735 for“Charger Portable Beam Processing Using a Cluster Source,” which isassigned to the assignee of the present invention. After the carbon isdeposited, the work piece is exposed to the reactants, and a pattern isformed by spontaneous deposition in regions where there is no carbon. Inanother embodiment, carbon or another material can be deposited globallyover the work piece surface, and then an electron or ion beam can removethe carbon or other material in a desired pattern before exposure of thework piece to the reactants. An initial pattern could also be created bylithography.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made to the embodiments described herein withoutdeparting from the spirit and scope of the invention as defined by theappended claims. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

We claim as follows:
 1. A method of depositing material onto a work piece in a vacuum chamber of a particle beam, comprising: providing within the vacuum chamber of a particle beam multiple gases that react with each other at a surface under reacting conditions to deposit a material onto a surface; providing a work piece having a surface that does not provide the reacting conditions; and directing a beam toward a portion of the work piece to provide at the portion of the work piece surface the reacting conditions to initiate deposition of the material onto the portion of the work piece surface by reaction of the multiple gases at the surface.
 2. The method of claim 1 in which the beam is discontinued whilst continuing to provide the multiple gases at the work pierce surface to continue to deposit material in the absence of the beam at positions at which the deposition was initiated.
 3. (canceled)
 4. The method of claim 1 in which the deposition is initiated whilst the work piece is maintained at a temperature of less than 100° C.
 5. (canceled)
 6. The method of claim 1 in which directing a beam toward a portion of the work piece to provide at the portion of the work piece surface the reacting conditions to deposit a material comprises directing a charged particle beam or a photon beam toward the work piece.
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. A method of depositing material onto a work piece, comprising: directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a deposition reaction and portions that do not support the initiation of the deposition reaction; and providing at the work piece surface multiple gases that react with each other to deposit a material at the regions at the surface that support the initiation of the deposition reaction to selectively deposit material in a pattern onto the work piece surface.
 11. The method of claim 10 in which the spontaneous deposition of material continues in the absence of directing the beam toward the work place.
 12. The method of claim 10 in which the deposition is initiated at room temperature.
 13. (canceled)
 14. The method of claim 10 in which the deposition is initiated whilst the work piece is maintained at a temperature of less than 200° C.
 15. The method of claim 11 in which the material that is spontaneously deposited supports subsequent spontaneous deposition.
 16. The method of claim 15 in which the deposition process is stopped by altering the concentration of the multiple gases as the work piece surface.
 17. The method of claim 10 further comprising directing an ion beam toward the work piece surface as the material is being deposited to increase the density of the material being deposited.
 18. The method of claim 10 in which directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a spontaneous deposition reaction and portions that do not support the initiation of the spontaneous deposition reaction includes directing an electron beam or an ion beam toward the work piece while providing at the work piece surface the multiple gases.
 19. The method of claim 10 in which directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a spontaneous deposition reaction and portions that do not support the initiation of the spontaneous deposition reaction includes directing an ion beam toward the work piece before providing at the work piece surface the multiple gases.
 20. The method of claim 10 in which directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a spontaneous deposition reaction and portions that do not support the initiation of the spontaneous deposition reaction includes directing a photon beam toward the work piece before providing at the work piece surface the multiple gases.
 21. The method of claim 10 in which directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a spontaneous deposition reaction and portions that do not support the initiation of the spontaneous deposition reaction includes directing a beam to deposit an initial layer onto the work piece, the initial layer supporting the initiation of the spontaneous reaction.
 22. The method of claim 10 in which directing a beam toward a work piece to prepare a work piece surface so that the work piece includes portions that support the initiation of a spontaneous deposition reaction and portions that do not support the initiation of the spontaneous deposition reaction includes directing a charge particle beam to deposit an initial layer onto the work piece, the initial layer inhibiting the initiation of the spontaneous reaction. 23-27. (canceled)
 28. The method of claim 1 in which providing a work piece having a surface that does not provide the reacting conditions further comprising heating the work piece above room temperature.
 29. (canceled)
 30. (canceled)
 31. The method of claim 10 in which the work piece is maintained at a temperature below the temperature of the walls of the vacuum chamber to cause the gases to preferentially react on the surface of the portion of the work piece.
 32. (canceled)
 33. The method of claim 10 further comprising stopping the reaction by reducing the partial pressure of one of the reaction gases.
 34. The method of claim 10 in which the material deposited has a resistivity of less than 2000 micro ohm-cm.
 35. The method of claim 34 in which the material deposited has a resistivity of less than 100 micro ohm-cm. 36-40. (canceled) 